1. Field of the Invention
The invention relates to a wireless local loop access network system, and more particularly to a wireless local loop access network system to which a public switched telephone network can be connected in the same conditions as conditions in which a public switched telephone network is connected to a wire access network.
2. Description of the Related Art
In construction of subscriber's lines between an exchange station in a public switched telephone network and subscribers, a wireless local loop (WLL) system is recently often selected in place of a wire access system in which an exchange station and subscribers are connected to each other through a copper wire or an optical fiber. In a wireless local loop system, an interface for mobile communication, such as PDS, PHS or CDMA, is used in radio lines. A conventional telephone as a subscriber's terminal may be used by connecting a mobile communication terminal or a specific terminal thereto.
FIG. 1 is a block diagram of a conventional wireless local loop access network system.
The wireless local loop access network system 100 is comprised of a subscriber unit (SU) 2 acting as the CDMA radio interface between the wireless local loop access network system 100 and a subscriber's telephone 1, first and second nodes or base station transceivers (BTS) 3 and 7 acting as the CDMA radio interface between the wireless local loop access network system 100 and the subscriber unit 2, and a node or wireless local loop base station controller (WSC) 4 connecting to a node or local exchange (LE) 5 in a public switched telephone network 101 in accordance with an interface identified as V5.2.
The subscriber's telephone 1 and the subscriber unit 2 are connected to each other through a copper wire acting as an analog interface, and both are set in a subscriber's house 102.
Though the illustrated wireless local loop access network system 100 includes the first and second base station transceivers 3 and 7, it is assumed herein that the subscriber unit 2 makes communication with the first base station transceiver 3.
The first and second base station transceivers 3 and 7 are connected to the base station controller 4 through an El interface and a program inherent to the wireless local loop access network system 100, as an upper layer of the El interface.
In the conventional wireless local loop access network system 100 illustrated in FIG. 1, the local exchange 5 has to operate taking into consideration that a subscriber is connected to the wireless local loop access network system 100 through a radio interface, in order to convert between a subscriber identifier corresponding to a protocol between the wireless local loop access network system 100 and the public switched telephone network 101, and a subscriber identifier in a radio protocol.
In addition, the subscriber unit 2, the base station transceiver 3, and the base station controller 4 have to include a specific structure for the same reasons as mentioned above.
Furthermore, the conventional wireless local loop access network system 100 is accompanied with a problem of an overhead in data access.
Japanese Unexamined Patent Publication No. 9-214467 has suggested a base station used in CDMA wireless local loop system. The base station uses diffusion codes perpendicular to each other in links in forward and reverse directions between the base station and a subscriber station. The base station includes a controller which controls a subscriber station such that a signal received from the subscriber station is in synchronization with the diffusion codes in a chip period.
Japanese Unexamined Patent Publication No. 9-247755 has suggested a wireless access system for connecting a public switched telephone network to a subscriber's terminal through radio signals. The subscriber's terminal includes a first detector which detects a non-telephone signal, and a first controller which transmits a detection signal indicative of detection of the non-telephone signal, through a control channel, and transmits the non-telephone signal through a data channel, bypassing a voice code decoder. Between the base station and the public switched telephone network is arranged a second controller which transmits the non-telephone signal transmitted through the data channel, to the public switched telephone network, bypassing a second voice code decoder, when the above-mentioned detection signal has been detected.
Japanese Unexamined Patent Publication No. 11-8694 has suggested an exchange arranged in a network in which a plurality of exchanges are connected to one another. The exchange includes a virtual access network unit which causes a second exchange to deal with communication of a subscriber to be managed by the exchange, a memory storing data indicating whether a subscriber to be managed by the exchange makes use of the virtual access network unit, and means for assigning a certain subscriber among subscribers to be managed by the exchanger, to the virtual access network unit, based on the data stored in the memory.
Japanese Unexamined Patent Publication No. 11-122667 has suggested a method of relaying communication in a system including base stations each making radio communication with a plurality of subscriber's terminals, a base station controller which controls the base stations, and a relay unit connected between the base stations and the base station controller. In the method, the relay unit and the base station controller are connected to each other through lines smaller in the number than lines through which the relay unit is connected to the base stations. The base station controller is relayed to the base stations in accordance with the number of assigned channels which number is set by the relay unit for each of the base stations.